1. Field of the Invention
This invention relates to fluid control valves, and more particularly, to a gate valve for use in both normal and relatively high temperature and/or high pressure environments.
2. Description of the Prior Art
Gate valves and other types of fluid control valves with annular resilient seals are well known and commonly used for controlling the flow of various fluids at ambient or moderate temperatures and at moderate pressures in a wide variety of industries. Such control valves commonly have a generally annular body defining inlet and outlet conduits with a chamber therebetween. A gate having an opening therethrough is disposed in a gate seat mounted within the chamber with the gate connected to a gate valve stem for movement between an open position in which flow is allowed through the conduits and the gate opening, and a closed position in which the flow is blocked by the valve gate. Gate seats mounted in an enlarged portion of the inlet and the outlet conduits adjacent the valve gate provide sealing between the valve gate and each of the adjacent conduits. Any fluid which leaks into the body chamber is prevented from leaking out around the valve stem by resilient packing and by an O ring positioned between the valve stem and a valve bonnet which is mounted atop the valve body to enclose the valve chamber. Such valves function quite satisfactorily at moderate temperatures and pressures, but the packing around the stem can be damaged by extremely high temperatures or pressures in the body chamber and can result in leakage of fluid from the valve.